1.1    介紹

每一個c程式都有個main函式，作為程式啟動入口函式。main函式的原型是int main(int argc , char *argv[]);其中argc表示命令列引數的個數；argv是一個指標陣列，儲存所有命令列字串。Linux程序名稱是通過命令列引數argv[0]來表示的。

Linux 還有環境變數引數資訊，表示程序執行需要的所有環境變數資訊。通過全域性變數

Char **environ;可以訪問環境變數。

命令列引數argv和環境變數資訊environ是在一塊連續的記憶體中表示的，並且environ緊跟在argv後面。如下圖：

1.2    驗證argv和environ執行連續記憶體的測試程式

1 #include <stdio.h>
  2 #include <string.h>
  3
  4 extern char **environ;
  5 int main(int argc , char *argv[])
  6 {
  7    int i;
  8
  9    printf("argc:%d\n" , argc);
 10
 11    for (i = 0; i < argc; ++i){
 12        printf("%x\n" , argv[i]);
 13        printf("argv[%d]:%s\n" , i , argv[i]);
 14     }
 15
 16    printf("evriron=%x\n" , environ[0]);
 17
 18    return 0;
 19 }
 

[email protected]:~/test#gcc -o test main.c

[email protected]:~/test#./test -p /usr/local/nginx -n 32

argc:5

bfa0c8f2

argv[0]:./test

bfa0c8f9

argv[1]:-p

bfa0c8fc

argv[2]:/usr/local/nginx

bfa0c90d

argv[3]:-n

bfa0c910

argv[4]:32

evriron=bfa0c913

1.3    修改程序名稱

按理說，修改程序名稱，只需要修改argv[0]指向的記憶體的值為所需要的值即可。但是當我們要修改的值超過argv[0]所指向的記憶體空間大小時，再這樣直接修改，就會覆蓋掉一部分argv[1]的值，因為從上面的圖中，很容易就可以看出。

這時候，該怎麼做呢？

1、必須重新分配一塊連續的記憶體空間，把argv和environ的引數都複製到新的空間。

2、修改argv[0]為所需要修改的值。

1.4    Nginx的做法

 * To change the process title in Linux andSolaris we have to set argv[1]
 * to NULL and to copy the title to the sameplace where the argv[0] points to.
 * However, argv[0] may be too small to hold anew title.  Fortunately, Linux
 * and Solaris store argv[] and environ[] oneafter another.  So we should
 * ensure that is the continuous memory andthen we allocate the new memory
 * for environ[] and copy it.  After this we could use the memory starting
 * from argv[0] for our process title.
 *
 * The Solaris's standard /bin/ps does not showthe changed process title.
 * You have to use "/usr/ucb/ps -w"instead.  Besides, the UCB ps does not
 * show a new title if its length less than theorigin command line length.
 * To avoid it we append to a new title theorigin command line in the
 * parenthesis.
 */
 
extern char **environ;
 
static char *ngx_os_argv_last;
 
ngx_int_t
ngx_init_setproctitle(ngx_log_t *log)
{
    u_char      *p;
    size_t       size;
    ngx_uint_t   i;
 
    size = 0;
 
    for (i = 0; environ[i]; i++) {
        size+= ngx_strlen(environ[i]) + 1;
    }
 
    p = ngx_alloc(size, log);
    if (p == NULL) {
        return NGX_ERROR;
    }
 
   /*
   這是為了找出argv和environ指向連續記憶體空間結尾的位置，為了能處理argv[i]被修改後，指向非程序啟動時所分配的連續記憶體，而採用了下面的演算法。但是實際上，這樣還是處理不了這種情況。僅僅是個人愚見！！！
   */
    ngx_os_argv_last= ngx_os_argv[0];
 
    for (i = 0; ngx_os_argv[i]; i++) {
        if (ngx_os_argv_last == ngx_os_argv[i]) {
            ngx_os_argv_last= ngx_os_argv[i]+ ngx_strlen(ngx_os_argv[i]) + 1;
        }
    }
 
    for (i = 0; environ[i]; i++) {
        if (ngx_os_argv_last == environ[i]) {
 
            size= ngx_strlen(environ[i]) + 1;
            ngx_os_argv_last= environ[i]+ size;
 
            ngx_cpystrn(p, (u_char *) environ[i], size);
            environ[i] = (char *) p;
            p+= size;
        }
    }
 
    ngx_os_argv_last--;
 
    return NGX_OK;
}
 
 
void
ngx_setproctitle(char *title)
{
    u_char     *p;
 
#if (NGX_SOLARIS)
 
    ngx_int_t   i;
    size_t      size;
 
#endif
 
    ngx_os_argv[1]= NULL;
 
    p = ngx_cpystrn((u_char*) ngx_os_argv[0], (u_char*) "nginx: ",
                    ngx_os_argv_last- ngx_os_argv[0]);
 
    p = ngx_cpystrn(p, (u_char *) title, ngx_os_argv_last - (char*) p);
 
#if (NGX_SOLARIS)
 
    size = 0;
 
    for (i = 0; i < ngx_argc; i++) {
        size+= ngx_strlen(ngx_argv[i]) + 1;
    }
 
    if (size > (size_t)((char *) p - ngx_os_argv[0])) {
 
        /*
         * ngx_setproctitle() is too rareoperation so we use
         * the non-optimized copies
         */
 
        p = ngx_cpystrn(p, (u_char *) " (",ngx_os_argv_last - (char*) p);
 
        for (i = 0; i < ngx_argc; i++) {
            p= ngx_cpystrn(p,(u_char *) ngx_argv[i],
                            ngx_os_argv_last - (char*) p);
            p= ngx_cpystrn(p,(u_char *) "", ngx_os_argv_last - (char *) p);
        }
 
        if (*(p - 1) == ' ') {
            *(p- 1) = ')';
        }
    }
 
#endif
 
    if (ngx_os_argv_last - (char*) p) {
        ngx_memset(p, NGX_SETPROCTITLE_PAD,ngx_os_argv_last - (char*) p);
    }
 
    ngx_log_debug1(NGX_LOG_DEBUG_CORE, ngx_cycle->log, 0,
                   "setproctitle:\"%s\"", ngx_os_argv[0]);
}